using System;

using System.Linq; 

using System.Collections;

using System.Collections.Generic;       

using System.Data;

using System.Data.Linq;

using System.Data.DataSetExtensions;

using System.Xml;

using System.IO;

using System.Xml.Linq;

​

public class Program

{

    public static void Main()

    {           

        DataTable table = new DataTable();

        table.Columns.Add("userId", typeof(string));

        table.Columns.Add("createdTime", typeof(DateTime));

        table.Rows.Add(new object[] {"1",  DateTime.Now.Date.AddDays(2)});

        table.Rows.Add(new object[] {"4",  DateTime.Now.Date.AddDays(3)});

        table.Rows.Add(new object[] {"1",  DateTime.Now.Date.AddDays(2)});

        table.Rows.Add(new object[] {"3",  DateTime.Now.Date.AddDays(4)});

        var result = table.AsEnumerable().Where(u=> u.Field<DateTime>("createdTime") > DateTime.Now.AddDays(-7)) //subtract a week

            .GroupBy(g=> new { userid = g.Field<string>("userId") , span = g.Field<DateTime>("createdTime").Minute })

            .Select(g=> new { userid = g.Key.userid, count = g.Count()})

            .GroupBy(g=> g.userid ).Select(s=> new {userid = s.Key, count = s.Count()}); 

        foreach(var res in result)

        {

            Console.WriteLine("{0} - {1}", res.userid, res.count);

        }

    }

}

​

​